Type 2 Diabetes May be Linked to Colorectal Cancer in Men

Summary
Colorectal cancers can lead to health problems and even death. It is known that obesity and lack of exercise increase the risk of colorectal cancer. Moreover, it has been shown that diabetes is associated with an increase in risk for these cancers. The authors of this study analyzed data from a large group of patients to understand this association. They found that type 2 diabetes increased the risk of colorectal cancers moderately, though this association was limited to males alone. Additionally, insulin use in these patients increased this risk, though not significantly.

Introduction
The incidence of diabetes, along with the many complications associated with it, is increasing throughout the world. Recent evidence suggests that diabetes may also be a risk factor for colorectal tumors. It has been suggested that this association may be due to increase in blood sugar and in insulin levels, which act as promoters of cell growth. This study hoped to confirm the association between type 2 diabetes and colorectal cancer. In addition, the authors also examined the effect of insulin use on this association.

Methodology
* The patients included in this study were selected from the participants enrolled in the Cancer Prevention Study II (CPS-II) Nutrition Study. All patients were aged between 50 and 74 at the time of enrollment.
* The study period was from 1992/1993 to 2007.
* Questionnaires were given to patients at one to two yearly intervals. Data about medical history, lifestyle, weight, height, diet, cancer screening and detection and insulin use was collected from the answers provided.
* The incidence of colorectal cancer was noted in the participants.

Results
* Colorectal cancer was diagnosed in 1,567 men and 12,42 women over the study period. Of these, 227 men and 108 women had a pre-existing diagnosis of type 2 DM, while 59 men and 26 women reported using insulin.
* A history of type 2 diabetes was found to increase the risk of colorectal cancer by 24 percent in men. Also, this risk was found to increase with the duration of diabetes. No association was found between diabetes and colorectal cancer in women.
* Insulin use in men was associated with a higher risk of colorectal cancer. No such association was noted in the case of women.
* The risk of colorectal cancer was higher in individuals with a family history of the same.

Shortcomings/Next steps
The use of questionnaires influences the validity of data collected. Many cases with diabetes may have been missed, as the study used a self-reporting design. Data regarding the use of diabetes medications was not collected or studied in relation to colorectal cancer. Therefore, no conclusion can be drawn regarding the influence of degree of sugar control and the incidence of colorectal cancer. Also, the reason for the different results in the two genders is not clear. Further studies that focus on detailed blood sugar and insulin profiles and that evaluate other biochemical parameters may clarify these issues.

Conclusion
The results of this study indicate that high blood sugars and insulin use may act as promoters of colorectal cancer. It can be assumed, therefore, that maintaining normal glucose and insulin levels may be important for the prevention of colorectal tumors. For men who are at a risk for diabetes, or who have been diagnosed with the disease, it is yet another reason to strive for appropriate management of the disease. The management strategy could include weight management and giving up smoking.